Packaging material and products comprising indicia-former which changes from a first visual condition to a second visual condition and indicates a characteristic of the package contents

ABSTRACT

Packaging materials, in particular, film and products which comprise (a) a substrate and (b) an energy sensitive indicia-former. The film has at least one heat sensitive indicia-former on at least part of the film. The film comprises a thin film substrate which is substantially transparent to radiant energy. Associated with at least part of the film substrate is an absorbent material which is sufficiently opaque to radiant energy to absorb said radiant energy and convert the radiant energy into heat energy. The indicia-former undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy from the absorbent material. The film is used preferably as a shrink wrap of the open top of drink containers and to identify the contents of the container.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of copending U.S. patent application Ser. No.10/359,347, filed Feb. 5, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 10/183,415, filed Jun. 28, 2002, and which is also based on and claims priority from U.S. Provisional Application No. 60/302,232, filed Jun. 29, 2001. This application also claims the benefit under 35 U.S.C. § 119 of U.S. Provisional Application No. 60/387,366, filed Jun. 10, 2002. All of these applications are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention pertains generally to packaging material and products which comprise (a) a substrate; and (b) an energy sensitive indicia-former carried by the substrate. The invention also pertains, in particular, to the use of such indicia-former on containers, having the capability of indicating the contents of such containers.

BACKGROUND OF THE INVENTION

[0003] In numerous instances, products are made and packaged that do not have markings that would be useful, for example, to identify the product, parts of the product or how to use the product. This is also true for packaging. Product identifiers on packaging material such as labels require time to complete and affix to the package, particularly if used in fast food preparation.

[0004] In fast food outlets, convenience stores and the like, beverage dispensing machines are used which are capable of dispensing a number of beverages of different brands and flavors. These beverages are usually poured into disposable paper cups having advertising printed thereon, but bearing no markings to identify the cups' contents.

[0005] When a beverage order includes a number of different brands and/or flavors, it is extremely difficult to determine the contents of each cup by visual inspection. Identification is further complicated by the placement of thermoformed lids over the cups to prevent spillage.

[0006] As a consequence of this problem, mix-ups occur, resulting in customers getting the wrong beverage and not discovering the error until they taste the drink.

[0007] One way in which this confusion can be avoided is by using paper cups of different colors or having different designs or markings thereon. However, this requires a large inventory of cups, and the person filling the order must be attentive to selecting the appropriate cup in order to avoid the error of filling the selected cup with the incorrect beverage.

[0008] Other ways of solving this problem include the use of labels affixed to the outer surface of the container or thermoformed lids having manually deformable buttons identifying drinks of various kinds. A further approach is marking the identity of the drink onto the container or its lidding with a pen, i.e., by circling the drink type or checking a box or dot next to a specific drink type. These solutions require an inventory of container labels or lids and consistently attentive servers.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is an object of the invention to provide a product comprising a substrate and an energy sensitive indicia-former carried by said substrate that undergoes conversion from a first visual condition to a second visual condition.

[0010] It is another object of this invention to provide a packaging material which comprises such energy sensitive indicia-former. It is a further object of this invention to provide a packaging material which shrinks in a controlled fashion upon exposure to heat of appropriate intensity, i.e. a shrink wrap material, thereby serving as a replacement for plastic lids as closures for drink containers.

[0011] It is a further object of this invention to provide a closure which comprises as the energy sensitive indicia-former, thermochromic ink that is converted from a first visual condition, preferably a visually indistinct, low contrast condition, to a second visual condition, preferably a visually distinctive, high contrast condition, when undergoing a temperature change. The first visual condition is preferably white. The second visual condition is preferably black or another dark hue, so that the conversion from the first to the second condition is clearly visually perceptible, thereby enabling the use of the ink as a marker of the contents of the container to which the closure is applied.

[0012] It is a further object of this invention to provide a product, packaging material or container closure, as described above, including the energy sensitive indicia-former of the invention, which avoids conversion from the first visual condition to the second, distinctive visual condition upon incidental exposure to radiant energy of appropriate intensity to cause such conversion. In this way, one can avoid occurrence of undesired and possibly erroneous marking of the product, packaging material or container closure, as the case may be, especially where multiple indicia-formers are adjacent to one another.

[0013] These and other objects are achieved by the packaging material and products of the present invention which comprise (a) a substrate and (b) an energy sensitive indicia-former carried by the substrate, which undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy. A preferred embodiment of the invention is a flexible packaging material which comprises (a) a substrate that is substantially transparent to radiant energy, (b) an energy absorbent material associated with at least a portion of the substrate, the absorbent material being sufficiently opaque to radiant energy to absorb and convert radiant energy into heat energy, thereby raising the temperature of the absorbent material, and (c) an energy sensitive indicia-former carried by said substrate which undergoes conversion from a first visual condition to a second visual condition upon an increase in temperature resulting from exposure to heat energy from the absorbent material. In a preferred form, the packaging material is a flexible film used to cover open-top containers. Other aspects of the invention include a method of manufacturing the above-described packaging and open-top containers covered by the above-described closures, and a method of filling an open-top container with a beverage and sealing the container with such closures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 illustrates an Osram 100W 24V GY 6.35 lamp and an Ushio JC 24V-100W/G 6.35 lamp.

[0015]FIG. 2 illustrates a configuration used for the indicia-former.

[0016]FIG. 3 is a photograph of cups having closures embodying the invention as described in EXAMPLES 8-11.

[0017]FIG. 4 is a photograph of cups having closures embodying the invention as described in EXAMPLES 8 and 9.

[0018]FIG. 5 is a photograph of cups having closures embodying the invention as described in EXAMPLES 10 and 11.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The invention has many applications. These include use of the indicia-former in packaging, product marking, decorative and labeling material and as a barrier material to protect articles from damage from, for example, water, heat, cold and radiation. The products to be marked can be any product to which the indicia-former can be affixed. The packaging may be any material continuously used for packaging, such as paper, dimensionally stable materials such as cardboard and heat sensitive packaging such as polyurethane or transparent clam shells used to hold take-out food. The packaging material may also be a film, and preferably a flexible film.

[0020] The present invention will be described below with references to thin film closures which are preferably transparent. A particularly preferred type of film is shrink film, commonly referred to as “shrink wrap film.” It should be understood, however, that the packaging material of the invention may also be embodied in a variety of other forms, such as thermoformed lids, packaging for construction materials, paper goods and pharmaceutical containers.

[0021] End uses of these films include food packaging (for example, oxygen and moisture barrier bag for frozen poultry; prime meat cuts and processed meat and cheese products for preservation of freshness and hygienics) and non-food packaging (for example, “overwraps” for protecting goods against damage, soiling, tampering and pilferage) during transporting, distribution, handling and display. A typical end use is in retail sales where the films are wrapped air-tight around single or multiple items of compact disks, audio/video tapes, computer software boxes, magazines, confectionery, boxed products, single serve bowls, etc. Another common end use is in wholesale marketing, where multiple containers of bottled and canned goods such as beverages, condiments and personal hygiene products are sold in bulk. Yet another example is in courier shipping, where singular items of shrink-wrapped sporting goods and household appliances are safely transported without the need for bulky protective cardboard cartons.

[0022] The term “shrink film” refers to a plastic wrapping film which has the capability of shrinking when it is heated to near the melting point of the film. These films are commonly manufactured from plastic resins such as polyvinyl chloride (PVC); polypropylene (PP); linear-low density polyethylene (LLDPE); low density polyethylene (LDPE); high density polyethylene (HDPE); copolymers of ethylene and vinyl acetate (EVA); copolymers of ethylene and vinyl alcohols (EVOH); ionomers (e.g., SURLYN®, a registered trademark of E. I. duPont de Nemours and Co., Wilmington, Del.); copolymers of vinylidene chloride (e.g., PVDC, SARAN, a trademark of the Dow Chemical Company); copolymers of ethylene and acrylic acid (EAA); polyamides (PA); polyester, polystyrene, nylon and copolymers of ethylene and octene.

[0023] Film Substrate

[0024] Films particularly suitable for this purpose are flexible and substantially transparent to radiant energy. It will be appreciated by those skilled in the art that the thickness of the film can be varied without adversely affecting the operation of the present invention. For certain applications, when greater strength is required, substantial film thickness may be appropriate, such as 200-gauge (0.05 mm) and more. Considerations such as price, tear resistance, degree of shrink and clarity will affect the selection of an appropriate film and thickness to suit the commercial objective to be met. When used in contact with food or beverage products, the film should be approved by the appropriate regulatory authorities.

[0025] If the film is a shrink wrap film, the preferred shrink film substrate will have shrink characteristics suitable for the given packaging objectives. Some of these characteristics include the degree and orientation of the shrink and whether the shrink is to occur in both or only in one direction. Most common commercially available shrink film substrates are substantially transparent, meaning that light, infrared radiation and other forms of radiant energy pass through the substrate with very little, if any, absorption. In this case, substantially transparent means that at least 75% and preferably more than 90% of radiant energy passes through said film. Such transparency has led to the utilization of a heat absorbing medium, in physical contact with the film, to provide sufficient heat transfer to cause the desired shrink. A preferred film is a bi-axially oriented thin shrink film, having a preferred thickness of between approximately 50 to 150-gauge (0.0127 mm to 0.0381 mm) with the most preferred range being from 60 to 75-gauge (0.0152 mm to 0.0191 mm). Films meeting these specifications are a 75-gauge (0.0191 millimeter) CLYSAR® polyolefin shrink film sold by Bemis Corporation of Minneapolis, Minn., and a 75-gauge 0.0191 millimeter Exfilm™ polyolefin shrink film sold by Intertape Corp. of Bradenton, Fla.

[0026] An alternate film is a shrink film that is made of polyvinyl chloride and sold under the trade name #2024 REYNOLON®, a trade name of Reynolds Metals Company of Richmond, Va. Such films are disclosed in U.S. Pat. No. 6,291,037 B1 to Bakker, the contents of which are incorporated by reference herein.

[0027] Energy Absorbent Material

[0028] The energy absorbent material used in practicing this invention is a material which is adapted to be associated with at least a portion of the film substrate and is sufficiently opaque to absorb energy, preferably radiant energy. Radiant energy includes electromagnetic energy. See The Condensed Chemical Dictionary, 8^(th) Edition, Revised by Hawley, Gessner G. (Van Nostrand Reinhold Company, New York, 1971) p. 750, in which radiation is defined as “energy in the form of electromagnetic waves (also called radiant energy or light).” The energy absorbent material functions to convert radiant (electromagnetic) energy into heat energy, thereby causing an increase in temperature of the film.

[0029] The absorbent material may be formed on the film by a variety of well-known methods such as printing means (flexographic, rotogravure, screen, transfer, etc.), brushing, spray coating, electrostatic coating, electrodeposition coating, flow coating, roller coating, dip coating, and the like. Printing is the preferred method (e.g., using flexographic or rotogravure techniques). The energy absorbent material includes at least one radiant energy absorbing component such as carbon black, graphite, iron oxide or the like. It will be appreciated by those skilled in the art that while certain specific energy absorbing materials have been identified, other material will also be suitable. What is desired is that the energy absorption rate of the material be sufficient so that upon exposure of the material to radiant energy, the heat generated will cause the desired degree of shrinkage of the film substrate in a predetermined amount of time.

[0030] In some cases, such films may require special treatment to be made more adaptable to printing of the energy absorbent material thereon, such as the application of a charged electric field, known as corona treating, which is done before printing to ensure adhesion of the absorbent material, and its carrier vehicle, if any. Other methods of promoting adhesion of the absorbent material include flame treatment or chemical primer application. For other films, such as polyvinyl chloride shrink films, corona treating is not necessary for good printing results.

[0031] In an alternate embodiment, the absorbent material may be physically incorporated into the film substrate and absorbs the radiant energy from within the film. This latter approach is less preferred to printing the absorbent material onto the film, since incorporating the absorbent material into the film may change the heat shrink characteristics of the film, such as flexibility, degree of shrink and the like. The absorbent material also renders the film opaque, eliminating the possible advantage of a transparent window.

[0032] According to the present invention, radiant energy means energy which may be transmitted from a suitable source to the absorbent layer, where it is absorbed to produce heat. In a preferred embodiment, the radiant energy is infrared radiation, which is efficiently absorbed by the absorbent layer, but not the film. In this way, heat energy is provided directly to the heat shrinkable film, thus avoiding the necessity of using any other heating medium, such as hot water or air, as in the past to carry the heat to the film. Thus, radiant energy in this context means any form of radiant energy that is transmissible through a medium such as air, without being substantially absorbed thereby. In a preferred embodiment, the radiant energy is supplied by a halogen lamp.

[0033] Carbon black provides good results when incorporated as the energy absorbent material on or in the film substrate. In particular, carbon black responds readily to the radiant energy output of a halogen lamp, which emits energy primarily in the visible and near infrared spectrum. Carbon black is a standard pigment in printing inks. This combined ability to blend with existing printing inks, and to absorb radiant energy such as infrared radiation, makes it well suited for use in the present invention.

[0034] A preferred energy absorbing material is carbon pigment-containing black ink sold by Coates Ink, a division of Sun Chemical, under the trade name Brazilia TN15787. This ink is readily adapted for printing onto the film substrate. The Brazilia inks are available in many colors and are broadly usable as absorbing materials according to the invention if the ink meets the requirements specified hereinabove. In a preferred embodiment, a reflective coating, preferably composed of white ink, is overlaid on the energy absorbent material in an amount sufficient to provide appropriate contrast with the indicia-former, after it is caused to change from the first visual condition to the second visual condition, so that the latter is more easily observed. A preferred white ink is also sold by Coates Ink under the trade names Lunar TN12316 and Alfalam TN13090. The use of a white ink overlay depends on whether a black or white background is more effective in facilitating visual observation of the change in the indicia-former from a preferred low contrast, first visual condition to the high contrast, second visual condition.

[0035] Energy Sensitive Indicia-Former

[0036] As described hereabove, the energy sensitive indicia-former changes from one visual condition to a second visual condition. Change in visual condition would include but not be limited to change in appearance, hue, shade, perceptibility, including an enhancement in perceptibility, brightness, lightness, reflectiveness, absorptivity and color, including, for example, light gray to dark gray and white to black.

[0037] The preferred indicia-former is a thermochromic pigment or dye, which may be dispersed in a suitable carrier. These thermochromic materials are preferably used in-the form of a thermochromic ink incorporating a thermochromic pigment or dye in a carrier vehicle. The thermochromic ink may be applied to the film substrate by the methods identified above for applying the absorbent material to the substrate. The preferred method is printing the thermochromic ink onto the substrate. The energy sensitive indicia-former is preferably an irreversible thermochromic ink that undergoes a change from white to black when adequately heated. A preferred thermochromic ink, (sold by Sherwood Technologies Limited of Nottingham, UK under the trade name Sherwood Type 90) is white below about 90° C. and undergoes an irreversible color change to black above about 90° C. Those of ordinary skill in the art will understand there are a variety of ink systems comprising one or more inks that can function as the radiant energy absorbent material and as the heat sensitive indicia-former.

[0038] Those of ordinary skill in the art will understand that a variety of ink colors can be used to obtain satisfactory results with the present invention and that a variety of energy sensitive indicia-formers other than thermochromic ink can also be used. Other inks that can be used in the invention as indicia-former are photochromic ink and electrochromic ink, such as those disclosed in U.S. Pat. No. 5,830,529 to Ross, the entire disclosure of which is incorporated herein by reference. Of course, photochromic and electrochromic inks, when employed as the indicia-former, would not require an absorbent layer. Instead, the indicia-former would be exposed directly to energy capable of causing the desired visual transformation of the indicia-former. In addition, those of ordinary skill in the art will understand that it is not necessary to coat the entire film substrate with ink. Moreover, those of ordinary skill in the art will appreciate that ink patterns can be used in applying the indicia-former to the substrate.

[0039] Preferred Applications of Absorbent and Indicia-Former Layers

[0040] As noted above, in a particularly preferred embodiment relating to films used to cover drink containers, an absorbent material comprising an ink composition containing carbon black is printed onto the film substrate. In a particularly preferred embodiment, the ink composition is conveniently applied by means of flexographic printing to print a pattern of parallel dotted lines, occupying an area of about a {fraction (3/16)}″ diameter circle. The flexographic plate is designed to print 40 lines/inch, 20% screen. As this ink composition is black in appearance due to its carbon black content, white ink, for example, is applied over the portions of the black ink on which the indicia-former is to be located to show the contents of the container, in order to provide appropriate contrast for the indicia-former. Then the indicia-former is superimposed on the areas of white ink, preferably by printing.

[0041] There are, of course, numerous possible combinations of the absorbent layer, optional contrast layer and energy sensitive indicia-former that can be employed in carrying out the invention.

[0042] Those of ordinary skill in the art will understand that a variety of ink concentrations can achieve satisfactory results in the present invention. The second ink which acts as an energy sensitive indicia-former may be, as identified above, an ink that undergoes conversion from one color to another that contrasts with the color of the absorbent material upon a predetermined increase in temperature. Alternatively, it may be an ink that undergoes a different sort of visually observable conversion, such as a dye or luminescent pigment that is covered by a patch that disintegrates upon a specific increase in temperature. The requirements for the energy sensitive indicia-former are that they undergo a conversion from a first visual state to a second visual state upon exposure to appropriate energy, and that such changes in visual state or condition are perceptible to the human eye.

[0043] Radiant Energy Source

[0044] According to one embodiment of the invention, the radiant energy source produces radiant energy by emitting light having wave lengths in the visible and near infrared range. Those of ordinary skill in the art will understand that the wave length of the energy emitted by the radiant energy source is not particularly critical, provided that the absorbent material chosen is sufficiently absorbent within the range of the wave lengths emitted, so that conversion of the radiant energy into heat energy and increased temperature of the film is reasonably rapid.

[0045] A preferred radiant energy source is a conventional halogen lamp emitting light energy having wave lengths between about 600 nm to about 1400 nm. It has been found that tungsten halogen lamps are a preferred radiant energy source. However, those of ordinary skill in the art will understand that a number of different radiant energy sources are available which produce sufficient visible and near infrared radiation, such as xenon arc lamps. The energy source is preferred to have a total wattage of between 30 and 150 watts, and most preferably comprises one 100-watt bulb. The wattage should be chosen to provide sufficient energy to shrink the film without burning through the film. One radiant energy source that has been successfully used is an Osram 100 W 24V GY 6.35 lamp from Osram Sylvania, Inc., of Danvers, Mass.

[0046] The most preferred radiant energy source is an Ushio JC 24V-100 W/G 6.35 lamp from Ushiodenki Kabushiki Kaisha of Tokyo, Japan. The Ushio lamp appears to provide a more even distribution of radiant energy intensity across the target area than the Osram lamp. As shown in FIG. 1, the filament of the Osram lamp is a natural helix, while the filament of the Ushio lamp is a more complex shape that appears to more closely approximate a point source. The reflector assembly within the lidding device is designed to produce an even distribution of energy across a target area on the film, assuming that the energy comes from a point source. The element of the Ushio lamp approximates a point source more closely than the element of the Osram lamp. Evaluations, partially summarized in the following EXAMPLE, confirm that the Ushio lamp produces a more uniform energy distribution across the target area than the Osram lamp.

[0047] In a preferred embodiment, the invention is used on packaging film which shrinks to form at least part of the package when exposed to heat. The packaging film includes a thin film substrate that contracts or shrinks when heated and which is substantially transparent to radiant energy. The film also includes an absorbent material that is sufficiently opaque to radiant energy to absorb and transfer to the substrate enough heat energy to cause the substrate to shrink when the film is exposed to a source of radiant energy. In a particularly preferred embodiment, the packaging film performs the function of a beverage container lid.

[0048] In use, radiant energy is caused to impinge on the film covering the container. The film has several marking options, such as “SODA,” “DIET COLA,” and “WATER,” imprinted on the film. Next to each option is an indicia area having absorbent and thermochromic ink layers.

[0049] In a particularly preferred form, the marking options printed onto the film have absorbent, reflective or contrast-enhancing and thermochromic layers. Accordingly, after the container is filled with a specific beverage, radiant energy is directed to the film at the beverage option selected. The radiant energy may be directed by indexing a variable mask situated between the radiant energy source and the indicia-former. The radiant energy source may comprise one lamp or more than one lamp. The radiant energy mask may have one orifice or several orifices through which the radiant energy is directed to the film. If the radiant energy is directed to the film at the beverage option selected through one orifice, the radiant energy results in the heating of the absorbent material precisely at the beverage option selected and thereby causes a localized increase in temperature of the indicia-former identifying that option. The increase in temperature causes the indicia-former identifying that option to change color (e.g., from white to black). The resultant black marking identifies the option selected, thus indicating the contents of the container. As radiant energy is not directed at the indicia-formers identifying other drink options, those indicia-formers do not change color. Accordingly, the beverage option selected is identified by the color change of the particular indicia-former identifying that option.

[0050] For example, if the container is filled with diet cola, the radiant energy is directed to, and causes the indicia-former identifying “DIET COLA” to change color, preferably from white to black. In this embodiment, the indicia-former changes to a color that contrasts with the background, so that the mark formed is easily identifiable. The identification marking can take numerous configurations. Preferred configurations are a circle enclosing the letter “x,” a check mark, or even a word or words identifying the beverage. An illustration of one of these configurations, namely the circle enclosing the letter “x,” is shown in FIG. 2. Preferably, the source of the radiant energy is positioned about 0.5 inch away from the film. In a most preferred form, the film is 0.932 inch from the center of the lamp filament and 0.464 inch from the top of the lamp.

[0051] As stated above, the best results have been obtained using an Ushio JC 24V-100W/G 6.35 lamp as the energy source. In operation, a pulse-width modulated signal from a micro-controller is used to control the average voltage level of the radiant energy source. This allows the radiant energy source to be maintained in a continually pre-warmed state. In particular, the average voltage across the radiant energy source can be adjusted by varying the duty cycle of a high frequency signal, so as to control the radiant energy output.

[0052] The duty cycle may be kept at a relatively low pre-warm, e.g., 0 to 5%, to allow the radiant energy source to operate at a pre-warming level, and then turned on fully or pulsed at a higher duty cycle, e.g., 20 to 60% for a time of 0.25 to 0.35 seconds, to transmit a more intense level of energy to the film to convert the indicia-former from the first to the second visual condition. Preferably, pre-warming is conducted at a 3% duty cycle, with conversion of the indicia-former occurring at a 35% duty cycle for 0.330 seconds. The use of these preferred conditions is particularly advantageous as a more pronounced conversion from the first visual condition to the second visual condition is obtained. A more pronounced conversion is desirable not only to display the result intended, but also to avoid confusion due to the possibility that adjacent indicia-formers would coincidentally undergo conversion to some extent due to incidental exposure to the radiant energy source. Indeed, the coincidental conversion of adjacent indicia-formers can result from an exposure over several hours to a pre-warm duty cycle at 4%.

[0053] Alternatively, radiant energy can be directed to the film precisely at the beverage options not selected so that the beverage option selected would be the only option identified that did not undergo a change from one visual condition to a second visual condition. This process can be accomplished by directing the radiant energy through several orifices in the variable mask. The orifices are aligned to ensure that the radiant energy is directed to the film precisely at the indicia-former identifying the beverage options not selected.

[0054] In a preferred embodiment, this marking of the identification of the drink is carried out in the same sequence of operations during which the container is filled and the shrink wrap film cover is applied to the open top of the container; however, the energy source used for the marking operation is distinct from the energy source used to shrink wrap the cover over the open container.

[0055] The invention also includes a method of manufacturing the film of the invention. According to this method, an absorbent material is applied onto at least a portion of a thin film substrate which is substantially transparent to radiant energy. The absorbent material is sufficiently opaque to radiant energy to absorb radiant energy and convert it to heat energy. Then an energy sensitive indicia-former which undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy is applied onto the film substrate. The preferred methods of application are by printing.

[0056] The invention also is directed to drink containers covered by heat shrinkable flexible films. According to this embodiment of the invention, an open-top container is covered by a heat shrinkable, flexible packaging film having at least one heat sensitive indicia-former on the surface thereof. The film material comprises a thin film substrate which is flexible and contracts when heated, and which is substantially transparent to radiant energy, thereby remaining substantially unchanged by radiant energy. An absorbent material overlays at least a portion of the film substrate. The absorbent material is sufficiently opaque to radiant energy to absorb and convert radiant energy into heat energy. This heat energy causes the heat sensitive indicia-former carried by the film to undergo conversion from a first visual condition to a second visual condition. This change in visual condition preferably occurs at a temperature below that at which the film is caused to shrink.

[0057] The invention is further directed to a method of preparing and sealing beverage containers. According to this embodiment of the invention, an open-top container is filled with a beverage. The open-top container is then covered with the film of the invention. The film material is then subjected to energy, which is converted to heat energy. The heat energy causes the film material to shrink to form a seal over the open top, and the indicia-former is thereafter exposed to heat sufficient to transform it from the first visual condition to the second visual condition. Alternatively, the sealing step can be carried out simultaneously with or after the step of transforming the indicia former from a first visual condition to a second visual condition.

EXAMPLE 1

[0058] A test was performed to confirm the ability of the combination of the thermochromic and absorbing inks to form the indicia-former after it undergoes exposure to radiant energy in the form of a lightbulb. A 75-gauge CLYSAR film manufactured by Bemis Corporation was printed with an absorbent material consisting of a black ink that contains carbon pigment sold under the name Brazilia TN15787 by Coates Ink, a division of Sun Chemical. Then a white ink sold by Coates Ink under the trade name Lunar TN12316 was printed over discrete portions of the black layer of absorbent material to provide indicia areas showing the various types of drink options, resulting in each indicia area having a gray color which serves to provide a contrasting background for the indicia formed upon conversion to the second visual condition. Next, an indicia-former composed of a white thermochromic ink manufactured by Sherwood Technologies, LLD, Nottingham, UK, under the trade name Sherwood Type 90 was printed over each gray-colored indicia area. The resulting indicia areas were gray in color.

[0059] The film was exposed to a 350-watt halogen lamp. The radiant energy was absorbed by the black ink, heating the thermochromic ink and causing the thermochromic ink to turn from a lighter color to black.

EXAMPLE 2

[0060] The test procedure used in EXAMPLE 1 was repeated, except that additional white ink was provided for contrast on each indicia area, resulting in the indicia area having a white appearance relative to the gray appearance in EXAMPLE 1 above. Then the thermochromic indicia-former was added over the white layer and exposed to the same 350-watt halogen lamp, causing the indicia-former to change from white to black. Accordingly, the color change of the thermochromic ink in EXAMPLE 2 was more pronounced and easier to see

EXAMPLE 3

[0061] The film substrate was treated with the absorbent ink for radiant energy absorption, white ink to provide contrast and thermochromic ink as the indicia-former, as in EXAMPLE 1. The treated film was exposed to the 350-watt halogen lamp for 0.5 second at a distance of 0.5 inch. Following such exposure, the thermochromic layer changed from white to black.

EXAMPLE 4

[0062] A packaging film was prepared as in EXAMPLE 3. The period of exposure of the treated film to the 350-watt halogen lamp at a distance of 0.5 inch was changed from 0.5 second to 1.0 second. The resulting heat melted the film, causing a hole to form in the film, indicating over-treatment.

EXAMPLE 5

[0063] The printed film of EXAMPLE 1 was exposed to radiant energy from a 100-watt halogen lamp for 0.25 second. The halogen lamp was operating at 30% of full power (duty cycle energized 30% of the time during activation period). Radiant energy was applied to the film at a distance of 0.5 inch. These conditions resulted in the transformation of the thermochromic ink from white to black, without any noticeable deleterious effect on the thermochromic ink layer.

EXAMPLE 6

[0064] The printed film of EXAMPLE 2 was exposed to radiant energy from a 100-watt halogen lamp for 0.25 second. The halogen lamp was operating at 30% of full power (duty cycle energized 30% of the time during activation period). Radiant energy was applied to the film at a distance of 0.5 inch. These conditions resulted in the transformation of the thermochromic ink from white to black, without any noticeable deleterious effect on the thermochromic ink layer.

EXAMPLE 7

[0065] The printed film of EXAMPLE 1 was treated with the black energy absorbent ink, two layers of white ink for contrast and thermochromic ink. The thermochromic ink was applied in the configuration of a circle enclosing the letter “x.” The film was exposed to radiant energy from a 100-watt halogen lamp for 0.25 second. The halogen lamp was operating at 30% of full power (duty cycle energized 30% of time during activation period). Radiant energy was applied to the film of a distance of 0.5 inch. The condition resulted in the transformation of the thermochromic ink from white to black, resulting in a very distinct circle enclosing the letter “x.”

EXAMPLE 8

[0066] The film of EXAMPLE 1 was treated with a uniform layer of the black energy absorbent ink, two layers of the white ink superimposed on the absorbent layer for contrast and the thermochromic ink. The thermochromic ink was applied in the configuration of a circle enclosing the letter “x” at a line thickness of 0.015 inch. The treated film was pre-warmed by exposure to the radiant energy from an Osram 100 W 24V GY 6.35 halogen lamp operating at a 2% duty cycle. Then the film was exposed to the lamp for 0.25 second with the lamp operating at 35% of full power (duty cycle energized 35% of time during activation period). Radiant energy was applied with the film at a distance of 0.932 inch from the center of the lamp filament and 0.464 inch from the top of the lamp. These conditions resulted in the transformation of the thermochromic ink from white to black, resulting in a faintly visible circle enclosing the letter “x.”

[0067] Cups lidded with the film treated according to the conditions set forth in this EXAMPLE are aligned in the row marked “A” in photographs marked as FIGS. 3 and 4. In FIG. 3, the transformed circles enclosing an “x” are most clearly visible in the cup closure second to left (next to designation “COLA”) and on the right-hand side cup closure (next to designation “OTHER”). In FIG. 4, the transformed circle enclosing an “x” is visible on the left-hand cup closure at designation “DIET” and on the right-hand cup closure at the designation “COLA.”

EXAMPLE 9

[0068] The printed film of EXAMPLE 1 was treated with the black energy absorbent ink, two layers of the white ink superimposed on the absorbent layer for contrast and with the thermochromic ink applied over the contrast layers. The black ink was applied by means of flexographic printing to print a pattern of parallel dotted lines, occupying an area of about {fraction (3/16)}″ diameter circle. The flexographic plate is designed to print 40 lines/inch; 20% screen. The thermochromic ink was again applied in the configuration of a circle enclosing the letter “x” at a line thickness of 0.020 inch. The treated film was subjected to the same conditions of pre-warming and exposure set forth in EXAMPLE 8.

[0069] Cups lidded with the film treated according to the conditions set forth in this EXAMPLE are also shown in FIGS. 3 and 4, aligned in the row marked “B.” The designations of the circle enclosing an “x” are more visible in the closures of cups “B” than in the closures of cups “A.” This difference is particularly visible in the cup closures shown in FIG. 4. This result indicates that the use of the black absorbent ink with the screen pattern resulted in the transformed thermochromic ink being more visible and having greater contrast to the untransformed thermochromic inks.

EXAMPLE 10

[0070] The printed film of EXAMPLE 1 was treated in the same manner as described in EXAMPLE 8. The treated film was pre-warmed by exposure to the radiant energy from the 100-watt Osram 100 W 24V GY 6.35 halogen lamp operating at a 4% duty cycle. Then the film was exposed to the lamp for 0.25 second with the lamp operating at 27% of full power (duty cycle energized 27% of time during activation period). Radiant energy was applied with the film at a distance of 0.932 inch from the center of the lamp filament and 0.464 inch from the top of the lamp.

[0071] Cups lidded with the film treated according to the conditions set forth in this EXAMPLE are shown in FIGS. 3 and 5 aligned in the row marked “C.” A comparison of FIGS. 3 and 5 indicates that the transformed thermochromic ink designations of the circle enclosing an “x” are more visible in the covers of cups “C” than in the cup closures of row “A.” This result indicates that carrying out the pre-warming steps at a 4% rather than a 2% duty cycle, and the exposure step at a lower duty cycle of 27% rather than 35%, appears to deliver more energy to the film, as evidenced by darker thermochromic ink marks. However, the use of the solid black absorbent layers resulted in undesirable slight false positive marks, best observed in the FIG. 5 Sample, C right cup next to “DIET” and “OTHER,” whereas “COLA” was the only intended mark.

EXAMPLE 11

[0072] The printed film of EXAMPLE 1 was treated in the same manner as described in EXAMPLE 9. The treated film underwent the pre-warming and exposure steps using the same conditions set forth in EXAMPLE 10.

[0073] Cups lidded with the film treated according to the conditions set forth in this EXAMPLE are also shown in FIGS. 3 and 5 aligned in the row marked “D.” A comparison of FIGS. 3 and 5 indicates that the transformed thermochromic ink designations of the circle enclosing an “x” are more visible in the cup closures of row D than in the closures of rows A, B and C. The cup closures in row D did not show false positives. The result indicates the advantages of applying the black energy absorbent ink in a noncontinuous pattern when applying the base layer of the indicia-former, with the printing pattern described in EXAMPLE 9, rather than in a single uniform layer.

EXAMPLE 12

[0074] The printed film of EXAMPLE 1 was treated in the same manner as described in EXAMPLE 9. The treated film was pre-warmed by exposure to the radiant energy from the 100-watt Osram 100 W 24V GY 6.35 halogen lamp operating at a 3% duty cycle. Then the film was exposed to the lamp for 0.35 second with the lamp operating at a 27% duty cycle. Radiant energy was applied with the film at a distance of 0.932 inch from the center of the lamp filament and 0.464 inch from the top of the lamp.

[0075] A cup lidded with the film treated according to the conditions set forth in this EXAMPLE had a pinhole burn in the film at the “DIET” drink mark.

EXAMPLE 13

[0076] The printed film of EXAMPLE 1 was treated in the same manner as described in EXAMPLE 9. The treated film was pre-warmed by exposure to the radiant energy from a 100-watt Ushio JC 24V-100W/G 6.35 halogen lamp operating at a 3% duty cycle. Then the film was exposed to the lamp for 0.33 second with the lamp operating at a 40% duty cycle. Radiant energy was applied with the film at a distance of 0.932 inch from the center of the lamp filament and 0.464 inch from the top of the lamp.

[0077] Cups lidded with the film treated according to the conditions set forth in this EXAMPLE had no film burn-through. The transformed thermochromic inks were observed to be visible and have good contrast to the untransformed thermochromic inks than the transformed inks.

EXAMPLE14

[0078] The printed film of EXAMPLE 1 was treated in the same manner as described in EXAMPLE 13. The treated film underwent the pre-warming and exposure steps following the conditions set forth in EXAMPLE 13, except that the exposure duty circle was increased from 40% to 50%.

[0079] Cups lidded with the film treated according to the conditions set forth in this example were observed to have no film burn-through. The transformed thermochromic ink was observed to have the same results of high visibility and good contrast to the untransformed thermochromic ink as observed in the cups lidded with the film treated according to the conditions set forth in EXAMPLE 13.

EXAMPLE15

[0080] The printed film of EXAMPLE 1 was treated in the same manner as described in EXAMPLE 13. The treated film underwent the pre-warming and exposure steps using the same conditions set forth in EXAMPLE 13, except that the exposure duty cycle was increased from 40% to 60%.

[0081] Cups lidded with the film treated according to the conditions set forth in this EXAMPLE were observed to have signs of burn-through.

EXAMPLE 16

[0082] The printed film of EXAMPLE 1 was treated in the same manner as described in EXAMPLE 13. The treated film underwent the pre-warming and exposure steps using the same conditions set forth in EXAMPLE 13, except that the indicia areas were misaligned to the left and to the right of their ideal locations by {fraction (3/32)}″. Cups lidded with the misaligned film results were observed to have transformed ink having the same good visibility and good contrast to the untransformed inks as observed in the cups lidded with the film treated according to the conditions set forth in EXAMPLE 13. This result indicates that an even distribution of radiant energy and increased duty cycle will still produce a transformed thermochromic ink that is highly visible and has good contrast to the untransformed thermochromic inks, even if the film is misaligned.

EXAMPLE 17

[0083] The treated film of EXAMPLE 13 underwent the same pre-warming and exposure steps as set forth in EXAMPLE 13.

[0084] One of many cups lidded with the film treated according to this EXAMPLE was observed to have a burn-through on the “DIET” drink mark

EXAMPLE 18

[0085] The printed film of EXAMPLE 1 was treated in the same manner as described in EXAMPLE 13. The treated film underwent the pre-warming and exposure steps following the conditions set forth in EXAMPLE 13, except that in the exposure step the lamp operated at 35% of full power (duty cycle energized 35% of time during activation period).

[0086] Cups lidded with the film treated according to the conditions set forth in this EXAMPLE were observed to have a transformed thermochromic ink of similar high visibility and good contrast to the untransformed thermochromic inks that was observed in the cups lidded with the film treated in EXAMPLE 13.

[0087] Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and EXAMPLES be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims. 

We claim:
 1. A packaging material which comprises: a) a substrate; and b) at least one indicia-former carried by said substrate which undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy.
 2. The packaging material according to claim 1, wherein the material is flexible.
 3. The packaging material according to claim 1, wherein the material is dimensionally stable.
 4. The packaging material according to claim 1, wherein the packaging material includes an absorbent material which comprises at least one radiant energy absorbing component selected from the group consisting of carbon black, graphite and iron oxide.
 5. The packaging material according to claim 1, wherein the indicia-former undergoes a change in perceptibility.
 6. The packaging material according to claim 1, wherein the indicia-former undergoes a change in appearance.
 7. The packaging material according to claim 1, wherein the indicia-former undergoes a change in hue.
 8. The packaging material according to claim 1, wherein the indicia-former undergoes a change in shade.
 9. The packaging material according to claim 1, wherein the indicia-former undergoes a change in brightness.
 10. The packaging material according to claim 1, wherein the indicia-former undergoes a change in lightness.
 11. The packaging material according to claim 1, wherein the indicia-former undergoes a change in saturation.
 12. The packaging material according to claim 1, wherein the indicia-former undergoes a change in color.
 13. The packaging material according to claim 1, wherein the indicia-former undergoes a change in reflectiveness.
 14. The packaging material according to claim 1, wherein the indicia-former undergoes a change in absorbtivity.
 15. The packaging material according to claim 1, wherein the indicia-former undergoes a change from white to black.
 16. The packaging material according to claim 1, wherein the indicia-former undergoes a change from light gray to dark gray.
 17. The packaging material according to claim 1, wherein the indicia-former is configured to comprise a circle enclosing the letter “x.”
 18. The packaging material according to claim 1, wherein the indicia-former is configured to comprise a check mark.
 19. The packaging material according to claim 1, wherein the indicia-former is configured to comprise words identifying packaging contents.
 20. The packaging material according to claim 1, wherein the heat sensitive indicia-former comprises thermochromic ink.
 21. The packaging material according to claim 20, wherein the thermochromic ink undergoes conversion from one color to a second color upon exposure to heat energy from the absorbent material.
 22. The packaging material according to claim 21, wherein the thermochromic ink undergoes conversion from white to black upon exposure to heat energy from the absorbent material.
 23. The packaging material according to claim 20, wherein the thermochromic ink is applied onto the film substrate by printing.
 24. The packaging material according to claim 23, wherein the thermochromic ink is applied onto the film substrate by flexographic printing.
 25. A product which comprises: a) a substrate; and b) at least one indicia-former carried by said substrate which undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy.
 26. A flexible material which comprises: a) a thin film substrate which is substantially transparent to radiant energy; b) an absorbent material associated with at least a portion of the substrate, said absorbent material being sufficiently opaque to radiant energy to absorb said radiant energy and convert said energy into heat energy; and c) at least one indicia-former carried by said film substrate which undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy from said absorbent material.
 27. The flexible material of claim 26, wherein the absorbent material is in the form of a nonuniform layer.
 28. The flexible material of claim 27, wherein said nonuniform layer comprises parallel dotted lines.
 29. A heat-shrinkable flexible packaging film, said film having at least one energy sensitive indicia-former on the surface thereof, said film comprising: a) a thin film substrate which is flexible and shrinks when heated, and which is substantially transparent to radiant energy, thereby remaining substantially unchanged on exposure to radiant energy; b) an absorbent material associated with at least a portion of said substrate, said absorbent material being sufficiently opaque to radiant energy to absorb said energy and convert said radiant energy into heat energy, with said heat energy being transferred to said indicia-former; and c) said energy sensitive indicia-former carried by said film being caused to undergo conversion from a first visual condition to a second visual condition upon exposure to said heat energy.
 30. The packaging film according to claim 29, wherein the temperature at which the energy sensitive indicia-former undergoes conversion from one visual condition to another is lower than the temperature at which said film is caused to shrink.
 31. The packaging film according to claim 29, wherein the film substrate is selected from the group consisting of polyvinyl chloride, polyolefins such as polypropylene, linear-low density polyethylene, low density polyethylene, high density polyethylene, copolymers of ethylene and vinyl acetate, copolymers of ethylene and vinyl alcohols, isonomers; copolymers of vinylidone chloride, copolymers of ethylene and acrylic acid, polyamides, polyesters, polystyrene, nylon and copolymers of ethylene and octenes.
 32. The packaging film according to claim 31, wherein the film substrate is a polyvinyl chloride or a polyolefin.
 33. The packaging film according to claim 32, wherein the film substrate is a bi-axially oriented shrink film having a thickness of between about 0.0127 millimeters and about 0.0381 millimeters.
 34. The packaging film according to claim 29, wherein the absorbent material comprises at least one radiant energy absorbing component selected from the group consisting of carbon black, graphite and iron oxide.
 35. The packaging film according to claim 29, wherein the indicia-former undergoes a change in perceptibility.
 36. The packaging film according to claim 35, wherein the indicia-former undergoes an enhancement in perceptibility.
 37. The packaging film according to claim 29, wherein the energy sensitive indicia-former is an ink selected from the group of thermochromic pigment, thermochromic dye and thermochromic ink.
 38. The packaging film according to claim 37, wherein the energy sensitive indicia-former comprises thermochromic ink.
 39. The packaging film according to claim 38, wherein the thermochromic ink undergoes conversion from white to black upon an increase in temperature due to heat energy from the absorbent material.
 40. The packaging film according to claim 29, wherein the energy sensitive indicia-former is applied to the film substrate by printing.
 41. The packaging film according to claim 40, wherein the indicia-former is applied onto the film substrate by flexographic printing.
 42. The packaging film of claim 29, wherein the indicia-former is applied to the film surface by brushing.
 43. The packaging film according to claim 29, wherein the indicia-former is configured to comprise a circle enclosing the letter “x.”
 44. The packaging film according to claim 29, wherein the indicia-former is configured to comprise a check mark.
 45. The packaging film according to claim 29, wherein the indicia-former is configured to comprise words identifying package contents.
 46. The packaging film according to claim 29, wherein the absorbent material is in the form of a nonuniform layer.
 47. The packaging film according to claim 46, wherein said nonuniform layer comprises parallel dotted lines.
 48. A method of sealing a beverage in an open-top container, said method comprising the steps of a) filling the container with the beverage; b) applying over the open top of the container the heat-shrinkable flexible packaging film of claim 29; and c) exposing the film to at least one radiant energy source, resulting in the conversion of the radiant energy to heat energy that causes the film to shrink and seal the open top of the container and change the indicia-former from a first visual condition to a second visual condition.
 49. The method according to claim 48, wherein the radiant energy sources used to shrink and seal the film and to change the indicia-former from the first visual condition to the second visual condition are distinct.
 50. The method according to claim 48, wherein the radiant energy source is any form of energy that is transmissible through a medium such as air without being substantially absorbed thereby.
 51. The method according to claim 48, wherein the radiant energy source is a tungsten halogen lamp emitting light energy having wave lengths of between about 600 nm and about 1400 nm.
 52. The method according to claim 51, wherein the halogen lamp is an Ushio JC 24V-100W/G 6.35 lamp.
 53. The method according to claim 48, wherein the radiant energy source has an average voltage that can be adjusted by varying the duty cycle of a high frequency signal so as to control the radiant energy output.
 54. The method according to claim 53, wherein the duty cycle of the radiant energy source is kept between about 0% to about 5% to allow the radiant energy to operate at a pre-warming level and then the duty cycle is increased to about 20% to about 60% for a time of about 0.25 to about 0.35 seconds to transmit a more intense level of energy to the film to convert the indicia-former from the first visual condition to the second visual condition.
 55. The method according to claim 48, wherein the radiant energy source is a 100-watt halogen lamp.
 56. The method according to claim 55, wherein the 100-watt lamp is an Ushio JC 24V-100W/G 6.35 lamp.
 57. The method according to claim 54, wherein the duty cycle of the energy source is kept at about 3% to allow the radiant energy to operate at a pre-warming level, and then the duty cycle is increased to about 35% for 0.33 seconds to transmit a more intense level of energy to the film to convert the indicia-former from the first visual condition to the second visual condition.
 58. The method according to claim 57, wherein the radiant energy source is a 100-watt halogen lamp.
 59. The method according to claim 58, wherein the 100-watt halogen lamp is an Ushio JC 24V-100W/G 6.35 lamp.
 60. In combination, an open-top container, the open top of which is covered by a heat-shrinkable flexible packaging film, said film comprising: a) a thin film substrate which is flexible and shrinks when heated, and which is substantially transparent to radiant energy, thereby remaining substantially unchanged by radiant energy; b) an absorbent material associated with at least a portion of said substrate, said absorbent material being sufficiently opaque to radiant energy to absorb said radiant energy and convert said radiant energy into heat energy; and c) an energy sensitive indicia-former carried by said film and comprising an ink formulation which undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy converted from the exposure of the absorbent material to radiant energy.
 61. The combination of claim 60, wherein the indicia-former undergoes conversion at a temperature below that at which said film is caused to shrink.
 62. The combination of claim 60, wherein the absorbent material comprises at least one radiant energy absorbing component selected from the group consisting of carbon black, graphite and iron oxide.
 63. The combination of claim 60, wherein the indicia-former is selected from the group consisting of thermochromic pigment, thermochromic dye and thermochromic ink.
 64. The combination of claim 60, wherein the indicia-former is thermochromic ink.
 65. The combination of claim 60, wherein the open-top container is a beverage container.
 66. The combination according to claim 60, wherein the indicia-former is configured to comprise a circle enclosing the letter “x.”
 67. The combination according to claim 60, wherein the indicia-former is configured to comprise a check mark.
 68. The combination according to claim 60, wherein the indicia-former is configured to comprise words identifying beverage options.
 69. The combination according to claim 60, wherein the absorbent material is in the form of a nonuniform layer.
 70. The combination according to claim 69, wherein said nonuniform layer comprises parallel dotted lines.
 71. A method of manufacturing a flexible film packaging material, said method comprising the steps of: a) applying to a thin film substrate a radiant energy absorbent material being sufficiently opaque to radiant energy to absorb said radiant energy and convert said radiant energy into heat energy; and b) applying to the substrate of the film a heat sensitive indicia-former which undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy.
 72. The method according to claim 71, wherein application steps (a) and (b) are carried out by printing the radiant energy absorbent material and heat sensitive indicia-former onto the film.
 73. A heat shrinkable flexible packaging film, said film having at least one energy sensitive indicia-former on the surface thereof, said film comprising: a) a thin film substrate which is flexible and shrinks when heated, and which is substantially transparent to energy, thereby remaining substantially unchanged on exposure to energy; and b) said energy sensitive indicia-former carried by said film comprising an ink formulation which undergoes conversion from a first visual condition to a second visual condition upon exposure to energy.
 74. The heat shrinkable flexible packaging film according to claim 73, wherein the indicia-former is selected from the group consisting of photochromic ink and electrochromic ink. 